The present invention relates to Scanning Probe Microscopes (SPM) typified by Scanning Tunnel Microscopes (STM) and Atomic Force Microscopes (AFM).
Currently, Scanning Probe Microscopes (SPM) typified by Scanning Tunnel Microscopes (STM) and Atomic Force Microscopes (AFM) are widely used as means for monitoring the shape of the surface of microscopic materials. A SPM monitors shapes and properties of a material surface using mutual physical interaction between a probe and a sample surface and can monitor with a high degree of resolution down to orders of a few nanometers. In order to achieve high resolution, it is necessary to minutely drive the sample and the probe in the X, Y and Z directions, with this driving normally being carried out using a piezoelectric element. The most typical of such piezoelectric elements is the cylindrical piezoelectric element. A cylindrical piezoelectric element is provided with electrodes to which individual drive signals can be applied. This enables driving in each of the X, Y and Z directions using individual piezoelectric elements. This has the benefit of maintaining relatively substantial displacement in the X and Y directions. It is then possible to reproduce an image of observation for the shape etc. of the surface of the material by mapping drive signals for the X, Y and Z directions applied to these cylindrical piezoelectric elements in three dimensions. FIG. 13 shows a configuration for a related SPM utilizing a cylindrical piezoelectric element. A probe 52 is fitted to a cylindrical piezoelectric element 50 via a probe support table 51. Changes in the probe in response to physical mutual interaction with a sample 53 on a sample table 54 are detected by mutual interaction sensing means 55. The object that is actually detected by the mutual interaction sensing means 55 is deflection of the probe 52 in response to atomic force when the mutual interaction is atomic force, and is tunnel current flowing between the probe 52 and the sample 53 in the case of tunnel current. It is possible to monitor the shape etc. of the surface of the sample 53 by scanning the X and Y directions while controlling the amount of driving of the cylindrical piezoelectric element 50 in the Z direction in response to the output signal of the mutual interaction sensing means 55. This control is performed by a SPM controller 56 and outputting of the monitored image and overall operation is carried out by operation/display means 57.
This related SPM is effective as a means for monitoring the surface of microscopic regions due to its high resolution. However, in recent years, the desire to measure the shape of semiconductors and recording media using SPM to a greater degree of accuracy has increased. When a SPM is viewed as this kind of measuring device, precision of positioning and repeatability precision are insufficient. In the related art, scanning in the X and Y directions is open-loop controlled so that the position of the probe or sample is decided by displacement of a piezoelectric element in line with an applied drive signal. However, in reality, the extent of this displacement is not proportional to the drive signal due to the existence of hysterisis and non-linear actions, etc. This makes it difficult to determine the position of the probe. The actual shape of a monitored image obtained in this manner is therefore not reliably reproduced. In order to resolve this problem, the drive signal and displacement of the piezoelectric element are measured for related SPM and compensation is performed so that the piezoelectric element acts in a linear manner. However, with this method, the compensation depends on past results and although this alleviates the influence of large amounts of hysterisis, etc., it cannot be said to be sufficient to prevent errors in microscopic positioning. Further, hysterisis and non-linear operations are differences depending on variations in the material of the element, shape precision, and electrode precision, etc., and it is therefore necessary to obtain compensation coefficients for each element. Further, there are also problems where errors due to environmental conditions such as temperature and vibrations etc. change.
A case where the thickness of a cylindrical piezoelectric element is not even will now be considered as an example of a non-linear operation occurring due to the precision with which a shape is made. FIG. 14A is a cross-sectional view of a cylindrical piezoelectric element where the thickness of left and right elements is uniform, and FIG. 14B is a cross-sectional view of a cylindrical piezoelectric element where the thickness of left and right elements is not uniform. The piezoelectric element actually used is provided with a plurality of electrodes and extends and compresses in three dimensions but here, for simplicity, the piezoelectric elements in FIG. 14A and FIG. 14B are considered to have electrodes uniform in a plane going from inside to out and are considered to be extendable and compressible in a vertical direction only. In the case in FIG. 14A, when a potential is applied across inner and outer electrodes, the desired characteristic is that shown by the dashed line in FIG. 14A where there is displacement in only a vertical direction in order to extend the piezoelectric element in a uniform manner to both the left and the right. When the thickness of the element is not uniform as shown in FIG. 14B, even if the same potential as for FIG. 14A is applied, there is also displacement in a horizontal direction shown by the broken line due to the thin portion on the left side in FIG. 14B being more extended, i.e. even if the same potential is applied, there is not just the error occurring in the vertical direction, but also a substantial error in the horizontal direction. It is therefore clear that substantial errors occur when a shape image is obtained from just a drive signal using the kind of piezoelectric element shown in FIG. 14B as a probe microscope.
It is an object of the present invention to provide a scanning probe microscope capable of repeatedly reproducing images for the shape of a sample etc. with a high degree of accuracy without being influenced by the environment. A scanning probe microscope of the present invention therefore comprises displacement detection means capable of measuring displacement of the microscopic driving means in the X, Y and Z directions, and image correction means for recording values outputted by each displacement detection means as arrayed data during scanning of a sample with a probe, and making an image from the recorded arrayed data with the relative positions with respect to the X, Y and Z directions corrected.
With this configuration, the position of the probe or sample can be accurately detected without this depending on the material of the element, the precision with which the shape is made, or external environmental conditions. Actual shapes can therefore be reproduced in a highly precise manner. This configuration is extremely straight forward in that not only can it be achieved by merely adding displacement detection means and image correction means to the SPM configuration of the related art, but also none of the functionality of the related SPM is lost.